Synthesis of (4-bromophenyl)(4-piperidy)methanone-(Z)-O-ethyloxime and salts

ABSTRACT

In one embodiment, the present invention describes the synthesis of (4-bromophenyl) (4-piperidyl)methanone-(Z)-O-ethyloxime and its acid salts, and similar compounds, in high stereochemical purity.

FIELD OF THE INVENTION

This application specifically discloses a novel process to synthesize(4-bromophenyl) (4-piperidyl)methanone-(Z)-O-ethyloxime and its acidsalt in high stereochemical purity. It also generically discloses aprocess to prepare compounds similar to the above in high stereochemicalpurity. The invention additionally discloses a novel acid-inducedisomerization to prepare predominantly the Z-isomers of suchO-ethyloximes. This application claims priority from U.S. provisionalapplication, Ser. No. 60/329,562 filed on Oct. 15, 2001. The inventiondisclosed herein is related to that disclosed in the provisional patentapplication, Ser. No. 60/329,561 filed on Oct. 15, 2001.

BACKGROUND OF THE INVENTION

(4-Bromophenyl) (4-piperidyl)methanone-(Z)-O-ethyloxime hydrochloride(Formula I) is an intermediate used in the preparation of4-[(Z)-(4-bromophenyl)(ethoxyimino)methyl]-1′-[(2,4-dimethyl-1-oxido-3-pyridinyl)carbonyl]-4′-methyl-1,4′-bipiperidine(Formula II). The compound of Formula II is discussed in pending U.S.patent application, Ser. No. 60/329,566, (Attorney Docket No. CD01443P)filed of even date herewith.

The compound of Formula II is also disclosed in the commonly owned U.S.patent application, Ser. No. 09/562,815, filed May 1, 2000. That patentapplication discloses several novel antagonists of the CCR5 receptorwhich are useful for the treatment of AIDS and related HIV infections.CCR-5 receptors have also been reported to mediate cell transfer ininflammatory diseases such as arthritis, rheumatoid arthritis, atopicdermatitis, psoriasis, asthma and allergies, and inhibitors of suchreceptors are expected to be useful in the treatment of such diseases,and in the treatment of other inflammatory diseases or conditions suchas inflammatory bowel disease, multiple sclerosis, solid organtransplant rejection and graft v. host disease.

In view of the importance of antagonists of the CCR5 receptor, new,novel methods of making such antagonists and/or their intermediates arealways of interest.

SUMMARY OF THE INVENTION

In an embodiment, the present application teaches a novel, simpleprocess of making (4-bromophenyl)(4-piperidyl)methanone-(Z)-O-ethyloxime and its acid salt in highstereochemical purity and high yields. It additionally teaches a novel,simple process to synthesize a compound of Formula I in highstereochemical purity and, via that process, a method of making acompound of Formula II in high yields and high stereochemical purity.The term “high stereochemical purity” refers to at least about 90% ofthe desired isomer, which, in the present invention, is the Z-isomer ofthe compound of Formula I. Indeed, the stereochemical purity of thecompound of Formula I made by the inventive process typically exceeds95% of the Z-isomer. The term “high yields” refers to at least about 60%yield of the desired product. The inventive process to prepare thecompound of Formula I in such high stereochemical purity is alsogenerically suitable for making compounds structurally similar to thecompound of Formula I.

Thus, the present process comprises synthesizing a compound of thegeneral Formula VII from commercially available isonipecotic acid(Formula III):

The process of making a generic compound of the type of Formula VII froma compound of Formula III comprises:

(a) preparing the N-protected derivative (Formula IIIA) fromisonipecotic acid (Formula III):

where Y is a protecting group;

(b) converting the compound of Formula IIIA to its acid halide (FormulaIV):

(c) reacting said compound of Formula IV with a suitable halobenzene inthe presence of a suitable Friedel-Crafts catalyst to yield the compoundof Formula V:

where X is a halogen derived from said halobenzene;

(d) reacting the compound of Formula V with (a) a suitable alkoxyamineand (b) an acid followed by deprotection under basic conditions toprovide the compound of Formula VI as a mixture of the Z and E isomers:

and

(e) isomerizing the compound of Formula VI by treatment with a strongacid and simultaneously converting to the desired acid salt of FormulaVII with an enriched Z isomer, wherein the Z isomer predominates overthe E-isomer by at least a 90:10 ratio. The thus-obtained acid salt mayoptionally be converted to its free base by treatment with anappropriate base as one skilled in the art can appreciate.

The inventive process to make the compound of Formula VII has severaladvantages: it is economical, can be easily scaled-up and yields thedesired Z-isomer in high yields and in high stereochemical purity.

DESCRIPTION OF THE INVENTION

In one embodiment, the present invention discloses a novel, easy-to-useprocess for preparing the compound of Formula VII in high yields andhigh stereochemical purity. When X is Br and “Acid” is HCl in FormulaVII, the compound is the same as the compound of Formula I, which is anintermediate useful in the preparation of the compound of Formula II, asdisclosed in pending U.S. patent application, Ser. No. ______, (AttorneyDocket No. CD01443P) filed of even date herewith. The inventive processto prepare the compound of Formula VII is schematically described belowin Scheme I:

The compounds of the Formula VI and VII, and their isomers, are believedto be novel compounds. The identity of the moiety X in the Formulas V,VI and VII is the same. As stated above, the pure Z-isomer acid salt(Formula VII) may optionally be treated with an appropriate base andconverted to the free base of the Formula:

Step 4 in Scheme 1 above includes a novel acid-catalyzed isomerizationprocess to yield predominantly the Z-isomer. Preparation of syn- oranti- aminoaryl alkyl ketoximes from a mixture of isomers by acidcatalysis is discussed by T. Zsuzsanna et al, Hung.Magy.Km.Foly., 74(3)(1968), 116-119. The Z- and E-isomeric forms of[R-(Z)]-1-azabicyclo[2.2.1]heptan-3-one,O-[3-(3-methoxyphenyl)-2-propynyl]-oxime and their acid-catalyzedisomerization are discussed in U.S. Pat. No. 5,534,522. While thepreferred reagents and reaction conditions for the various steps in theinventive process are described in detail in the Examples section, thefollowing summarizes the details.

The presently disclosed process starts with the known compound ofFormula III, which is commercially available isonipecotic acid. In step1, isonipecotic acid is N-protected. The protecting group is introducedby reacting compound III with a suitable acid, acid chloride, acidanhydride, carboxylic ester, and the like, as is well known to thoseskilled in the art. Useful protective groups that may be employed aretrifluoroacetyl (—C(O)CF₃), acetyl (—C(O)CH₃), formyl (—CHO), —C(O)OEtand the like; preferred is trifluoroacetyl, introduced by reacting withtrifluoroacetic anhydride. The trifluoroacetic anhydride is employedgenerally in about 1 to about 5 molar equivalents (based on the moles ofisonipecotic acid), preferably in about 1 to about 3 molar equivalents,and typically in about 1.5 to about 2 molar equivalents. A solvent maybe employed such as, for example, hydrocarbons such as toluene, xyleneand the like, halogenated hydrocarbons such as, for example, methylenechloride, ethylene chloride, chloroform, chlorobenzene and the like,esters such as, for example, ethyl acetate, n-butyl acetate, isopropylacetate and the like, ethers such as, for example, tetrahydrofuran,diglyme and the like, ketones such as methyl ethyl ketone, methyl amylketone and the like, as well as mixtures of such solvents. Preferred arethe esters, especially isopropyl acetate. Generally, isonipecotic acidis dissolved, suspended or dispersed in the selected solvent andtrifluoroacetic anhydride is added and maintained at a temperature ofabout 0-30° C. for about 0.5-5 hours. After the reaction is complete,the product of Formula IIIA may be isolated by conventional processessuch as, for example, neutralization of any remaining acid and solventextraction.

The N-protected isonipecotic acid (IIIA) is then converted to its acidhalide (IV) by reacting with a suitable reagent such as, for example, athionyl halide, phosphoryl halide, oxalyl halide and the like; oxalylhalide, thionyl chloride is especially preferred. The acid halide may beemployed generally in about 1 to about 4 molar equivalents, preferablyin about 1 to about 3 molar equivalents, and typically in about 1 toabout 1.5 molar equivalents. The thus-prepared acid halide of Formula IVis then subjected to a Friedel-Crafts alkylation with a halobenzene inStep 2. Friedel-Crafts alkylation is well known in the art of organicsynthesis. Generally, the catalyst employed is typically a metal halidesuch as, for example, AlCl₃. Illustrative useful halobenzene isfluorobenzene, chlorobenzene, bromobenzene or iodobenzene, withchlorobenzene and bromobenzene being preferred. The halobenzene isemployed generally in about 3-8 volumes, preferably in about 3-7 volumesand typically in about 4-6 volumes, with respect to the compound of theFormula IV. The AlCl₃ catalyst is generally employed in about 2-5 molarequivalents, preferably in about 2-4 molar equivalents and typically inabout 2-3 molar equivalents with respect to the compound of Formula IV.Generally, the ingredients are mixed and maintained at a temperaturerange of 5-80° C. for about 1-5 hours. The product of Formula V afterwork-up is generally isolated by solvent extraction, precipitation orsimilar methods well known to those skilled in the art.

The compound of Formula V is then converted to an ethoxyoxime of FormulaVI by reacting it with ethoxyamine (or its hydrochloride), usually inaqueous solution form. Ethoxyamine (or its hydrochloride) is employedgenerally in about 1 to about 4 molar equivalents, preferably in about 1to about 3 molar equivalents, and typically in about 1 to about 2 molarequivalents. Generally, the reaction is catalyzed by a weak acid suchas, for example, acetic acid, formic acid and the like, or mixturesthereof, in a solvent such as, for example, methanol, ethanol,isopropanol, n-butanol and the like, or mixtures thereof. The product ofFormula VI, after work-up, is a mixture of the Z- and the E-isomers,whose ratio may be analyzed for its stereochemical make-up, usingtechniques well known in the art such as, for example, HPLC.

Since the desired isomer is the Z-isomer in compound VII, it would beadvantageous to enrich the compound of Formula VI in the desiredZ-isomer. Applicants found that treating the compound of Formula VI witha strong acid under certain reaction conditions surprisingly isomerizesthe mixture of the Z and the E-isomers into predominantly the Z-isomer.Generally, the compound of Formula VI may be dissolved in a solvent suchas, for example, ethanol, methanol, isopropanol, n-butanol and the like,ether such as methyl tert-butyl ether, tetrahydrofuran and the like,hydrocarbon such as, for example, heptane, hexane, toluene and the like,nitrile such as, for example, acetonitrile, benzonitrile and the like,or mixtures of such solvents. It is then treated with a strong acid suchas, for example, HCl, HBr, H₂SO₄ and the like, at temperatures in therange 10 to 80° C. for about 1-80 hours. The acid is employed generallyin about 1.1 to about 8 molar equivalents, preferably in about 1.1 toabout 6 molar equivalents, and typically in about 2 to about 4 molarequivalents. Work-up typically forms predominantly the acid salt of theZ-isomer of the compound of Formula VII. HPLC analysis (when X=Br andthe acid salt was HCl) after a typical reaction sequence as shown in theExamples section showed the presence of the Z-isomer generally in about90% or above stereochemical purity, and typically in about 95% or abovestereochemical purity. Additionally, the yields of the desired compoundin such stereochemical purity was quite high, demonstrating that suchisomerization reaction using a strong acid may be applicable to prepareZ-isomers of such oximes in high yields and high stereochemical purity.

The products of the various steps in the reaction schemes describedherein may be isolated and purified by conventional techniques such as,for example, filtration, recrystallization, solvent extraction,distillation, precipitation, sublimation and the like, as is well knownto those skilled in the art. The products may be analyzed and/or checkedfor purity by conventional methods such as, for example, thin layerchromatography, NMR, HPLC, melting point, mass spectral analysis,elemental analysis and the like, well known to those skilled in the art.

The following nonlimiting EXAMPLES are provided in order to furtherillustrate the present invention. While the EXAMPLES are describedherein as the preparation of the compound of Formula I from the compoundof Formula III, it will be apparent to those skilled in the art thatmany modifications, variations and alterations to the presentdisclosure, both to materials, methods and reaction conditions, may bepracticed. All such modifications, variations and alterations areintended to be within the spirit and scope of the present invention.

EXAMPLES

Unless otherwise stated, the following abbreviations have the statedmeanings in the Examples below:

HPLC=High Performance Liquid Chromatography

M.pt: melting point

NMR=nuclear magnetic resonance spectroscopy

DMSO=dimethylsulfoxide

mL=milliliters

g=grams

rt=room temperature (ambient)

Example 1

Preparation of Compound of Formula IV from a compound of Formula III:This compound was prepared by following a procedure similar to M. F.Hibert et al., J. Med. Chem., 33 (1990), 1594-1600. To a suspension of440 g of isonipecotic Acid in 1760 mL of isopropyl acetate at 0-10° C.was added 880 mL of trifluoroacetic Acid over at least 2 h , whilemaintaining the temperature below 30° C. After complete addition, thereaction mixture was heated to 55-65° C. After about 2 h, the reactionmixture was cooled to about room temperature, and 1760 mL of isopropylacetate was added. The reaction mixture was cooled to between −10° C.and 0° C., whereupon 1320 mL of water was added while maintaining thetemperature below 15° C. This was followed by the addition of 1364 g of25% sodium hydroxide solution while maintaining the temperature below15° C. The biphasic mixture was stirred for about 3 h at roomtemperature. The aqueous layer was removed, and was extracted with 880mL of isopropyl acetate. The combined isopropyl acetate solution waswashed twice with 880 mL of a 15% sodium chloride solution each time.The reaction mixture was concentrated to about 1320 mL. Upon cooling,the product started to crystallize. The mixture was cooled to roomtemperature and 1760 mL of heptane was added. The suspension was cooledto between −5° C. and 5° C., stirred for 1 h, and then filtered. Thecollected solid was washed with 440 mL of heptane, and then dried undervacuum at 55-65° C. to give 613.6 g of the compound of Formula IV, mp:113.5° C.

Example 2

Preparation of Compound of Formula V from a compound of Formula IV: To asuspension containing 477 g of the compound of Formula IV in 1900 mL ofbromobenzene was added 257 g of thionyl chloride. The reaction mixturewas heated to 60-65° C. over about 1 h. After another 1-2 h, thereaction mixture was cooled to 10-15° C., whereupon 588 g of aluminumchloride was added in 5 portions. During each addition, the temperaturewas maintained between 10-15° C. After the addition of aluminum chloridewas complete, the reaction mixture was heated to 65-70° C. over a 3 hperiod. After about 1 h, another 70 g of aluminum chloride was added.After about 1 h, the reaction mixture was transferred to 2370 mL of a 6N hydrochloric acid solution pre-cooled to between 5° C. and 10° C.During the transfer, the temperature was maintained below 40° C. Thereaction flask was rinsed with 470 mL of bromobenzene and 470 mL ofwater. The biphasic mixture was separated. The organic solution wasconcentrated under reduced pressure to about 820 mL. To this mixture wasadded 1320 mL of methyl tert-butyl ether, and 1790 mL of heptane. Aftercrystallization has started, another 860 mL of heptane was added. Thesuspension was cooled to between 0-5° C., stirred for at least 30 min,and the filtered. The collected solid was washed with 530 mL of coldheptane, dried under vacuum at 40-50° C. to give 537 g of the ketonecompound of Formula V, m.pt: 96.1° C.

Example 3

Preparation of Compound of Formula VI from a compound of Formula V: Asolution containing 293 g of the compound of Formula V, 336 g of 30%aqueous ethoxyamine solution, and 9 mL of acetic acid in 1170 mL ofmethanol was kept under reflux at about 65° C. for about 3 h. Thereaction mixture was cooled to room temperature, and a solution of 450mL of 25% sodium hydroxide was added. The biphasic mixture wasvigorously stirred. After at least 10 min, the reaction mixture is addedto a mixture of 1470 mL and 1470 mL of methyl tert-butyl ether. Thelayers were separated, and the organic layer was washed with 147 mL ofwater, followed by 147 mL of a 10% sodium chloride solution. The organicsolution was concentrated to about 730 mL. The concentrate was dilutedwith 880 mL of methyl tert-butyl ether and concentrated again to about730 mL. The distillation was repeated again with 880 mL of methyltert-butyl ether, and the concentrate was used in the next step directlywithout additional purification.

Example 4

Preparation of Compound of Formula I from a compound of Formula VI withZ-isomer predominance: Into a solution of the compound of Formula VI(600 mL of total solution including 247 g of active component in methyltert-butyl ether as prepared in Example 3) was charged 758 mL ofisopropyl alcohol (“IPA”) and 2280 mL of methyl t-butyl ether (“MTBE”).An anhydrous IPA solution of HCl (4.8 N, 382 mL) was added dropwise. Theresulting slurry was stirred for 12 h and then cooled to 0° C. Afterstirring 2 h, the crude product was filtered and washed with 200 mL of1:2 of IPA and MTBE followed by 200 mL of MTBE. The resulting crudeproduct was dried under vacuum at 55° C. for 2 days to give white solid(294 g, 92%). This crude product was found to contain 91:9 ratio of theE and Z-oximes respectively by HPLC analysis. The crude mixture wasadded into a 5 L round-bottomed flask followed by 1420 mL of IPA and1420 mL of MTBE and then heated to 65° C. The resulting slurry wasagitated by using mechanical stirrer for 68 h and then cooled to 10° C.After stirring 2 h, the final product was filtered and washed with 370mL of 1:2 of IPA and MTBE followed by 370 mL of MTBE. The product ofFormula I was dried under vacuum at 55° C. to give white solid (258 g,90% yield, 96:4 ratio of E and Z-oxime respectively, by HPLC analysis).¹H NMR (400 MHz, DMSO-d6) the major product after isomerization(Z-oxime): δ 8.99 (bs, 2H), 7.63 (d, J=8.4, 2H), 7.27 (d, J=8.4, 2H),3.99 (q, J=7.0, 2H), 3.24-3.21 (m, 2H), 2.90-2.84 (m, 3H), 1.85-1.82 (m,2H), 1.71-1.64 (m, 2H), 1.12 (t, J=7.0, 3H); minor (E-oxime): δ 7.60 (d,J=8.4), 7.44 (d, J=8.4), 4.13 (q, J=7.0), 1.25 (t, J=7.0).

1-40. (canceled)
 41. A compound of the Formula:

wherein said compound contains an enriched Z-isomer, with the Z-isomerpredominating over the E-isomer by at least about a 90:10 ratio, withsaid compound being prepared bv a process comprising: (a) convertingisonipecotic acid (Formula III) to its N-protected derivative (FormulaIIIA):

where Y is a protecting group; (b) converting the compound of FormulaIIIA to its acid halide (Formula IV):

(c) reacting said compound of Formula IV with a suitable halobenzene inthe presence of a suitable Friedel-Crafts catalyst to yield the compoundof Formula V:

where X is a halogen; (d) reacting the compound of Formula V with analkoxyamine and an acid, to provide the compound of Formula VI as amixture of the Z and E isomers:

(e) isomerizing the compound of Formula VI by treatment with a strongacid and simultaneously converting to the desired acid salt of FormulaVII with an enriched Z isomer, wherein the Z isomer predominates overthe E-isomer by at least about a 90:10 ratio; and (f) reacting said acidsalt in step (e) with a base to form a free base of the formula:

wherein said free base contains an enriched Z-isomer, with the Z-isomerpredominating over the E-isomer by at least about a 90:10 ratio.
 42. Thecompound of claim 41, wherein X=Br.
 43. A compound of the Formula:

including isomers of said compound.
 44. A compound of the Formula:

including isomers of said compound.